just found out if they spin opposite, it means regular, non-posi. also I was told that there wasnt any 9" posi rears, that if they spin the same way, it's because they were more than likely modified and welded togeather. but there was limited slip....just not true posi. was also told that if I really wanted to know about the spline, I would need to pull it apart to be 100% sure.